I don’t think you realize the scope of the German army simply being placed in France/Italy.
Look at Sicily where Hube got away with a minor army and then held off the Allies in Italy till the end of the war. If Allies try to invade through the Balkans the results would be even worse because the mountains in Greece are even worse than those in Italy.
So, we have France.
The beaches now have triple, maybe quadruple the defence they had in ‘real’ history + a constant flow of armor divisions and a strong Luftwaffe (the only reason the Germans lost the Battle of Britain was because Goring changed the gameplan too many times and –- yup — planes were needed to invade Russia; so what if the Germans never pulled back their attacks…?).
Germany bumps up their rocket development from the bottom of the list and maybe the Panther-tank is never produced (t’was a counter to the T-34, but since the Russians aint fighting Germany…) but the Me-262 comes out in '43/'44… Allied air-superiority is practically crushed right there and then.
The Allies could barely beat Rommel in the desert (an open playing field) despite having numerical superiority in every aspect (manpower, airpower, tanks, supplies) — so what if the Germans deploy more tank divisions in Africa because there wouldn’t be a war with Russia? Think the measly M3-Lees/Grants had a tough time with Pz IVs? What about some StuGs and even more Tigers (they already had two battalions there)? Air superiority?
We’re talking about the ENTIRE German army here plus any advances they were planning to make but couldn’t execute BECAUSE of Russia (rockets, jet-aircraft, nukes?). Germany could easily invade the Arabic lands from Egypt and have all the supplies necessary to continue their war to an eventual invasion of Britain (perhaps in '40/'41).
Russia is what wrought the end of Germany — without that harbringer sucking supplies, engineering, and manpower Germany could easily steamroll all other opponents in Europe/Africa. If anyone thinks otherwise you are really not thinking hard enough on it (or just lack the knowledge thereof).